1. Field of the Invention
The present invention generally relates to a roll-sheet feeding device that feeds a roll-sheet type medium such as a roll sheet wound in a roll, and an image forming apparatus having the roll-sheet feeding device such as a printer, a plotter, a facsimile machine, and a copier.
2. Description of the Related Art
There are a large-scale copiers that handle large size drawing documents such as those of A0 or A1 size, and electrophotographic image forming apparatuses such as a printer, or other types of printers that generally form images on a large size sheet medium. Such image forming apparatuses include a roll-sheet feeding device, which generally employs a roll sheet as a sheet medium and transfers the roll sheet to an image forming unit to improve the convenience of handling the sheet type medium. The roll sheet is configured to include a sheet tube used as a roll core around which a long paper-sheet is rolled. In the roll-sheet feeding device, the roll sheet is rotationally supported such that the sheet is fed to the image forming unit at a predetermined linear speed based on the rotational speed of the roll sheet.
The related art supporting types that can rotationally support the roll sheet in the roll-sheet feeding device include a spool type sheet support or a flange type sheet support to accommodate various sizes of roll sheets.
In the spool type sheet support, spool is placed in the sheet tube to enable the roll sheet to rotate. In the spool type sheet support, when an unwind mechanism for rewinding the roll sheet is provided in the roll-sheet feeding device, a drive transmission mechanism can be easily provided on the spool to rotationally drive the roll sheet easily in the roll-sheet feeding device. At the same time, however, when replacing the roll sheet, a user has to place the long spool in the roll sheet, which may impose a cumbersome operation on the user.
By contrast, in the flange type sheet support, flange members are inserted from both ends of the sheet tube and the flange members are rotationally supported in the roll-sheet feeding device to enable the roll sheet to rotate. In the flange type sheet support, the user has to only insert the flange members from both ends of the roll sheet when replacing the roll sheet, and thus the flange type sheet support provides a superior operability for the user.
In the flange type sheet support, drive force can be directly transmitted to the roll sheet in a manner such that an outer diameter of the flange member is made larger than a maximum outer diameter of the roll sheet. Note that the maximum outer diameter of the roll sheet means the roll sheet indicates an outer diameter of the roll sheet having a maximum amount of remaining roll sheet.
In addition, Japanese Patent Application Publication No. 2003-276264, for example, discloses a roll-sheet feeding device having a flange type sheet support in which the outer diameter of flange members is made smaller than the maximum diameter of the roll sheet, and the flange members are rotationally supported by receiving rolls, thereby enabling the roll sheet to rotate in the roll-sheet feeding device.
However, the roll-sheet feeding device having the above flange type sheet support has the following drawbacks.
In image forming apparatuses including inkjet printers, a roll sheet may have to be intermittently transferred while forming images. When the roll sheet is intermittently transferred, the roll sheet is transferred in a progressive (winding) direction due to inertia, which may make the roll sheet loose. Thus, there may need some looseness prevention device to prevent the roll sheet from being loosened in the roll-sheet feeding device. For preventing the roll sheet from getting loose, the roll-sheet feeding device may need to include a pulling mechanism working as a brake by which the roll sheet is pulled in a rewinding direction opposite to the winding direction to cancel out the inertia of the roll sheet. The pulling mechanism may include a mechanism to generate load (load generating mechanism), such as rotational load, as a pulling force generating mechanism.
However, when the load generating mechanism generating large load is provided in the roll-sheet feeding device for preventing the roll sheet from being loosened, brake force of a large rotational load generated by the load generating mechanism may exceedingly be imposed on a drive source that transfers the roll sheet in a sheet feeding direction. As a result, an electric motor of the drive source need be increased in size, which results in large power consumption.